1. Field of the Invention
The present invention relates to a power supply monitor circuit of a hard disk drive and, more particularly, to a method for reducing a malfunction generated by a variation in a power supply voltage due to excessive current drawn when driving a spindle motor.
2. Description of the Related Art
Typically, a hard disk drive system combine a hard disk assembly (HDA) consisting of mechanical elements with a printed circuit board (PCB) consisting of circuit elements. Since the hard disk drive can access a large amount of data at a high speed by magnetically writing/reading data in/from a rotating magnetic disk, it is widely used as an auxiliary memory unit of a computer system. The hard disk drive uses a power supply monitor circuit to determine whether a supplied power supply voltage is normal or abnormal. A power supply monitor circuit monitors power supply voltages of 12V and 5V, and supplies an output PF of a logic "HIGH" level to a controller, for example, a central processing unit (CPU) when the power supply voltages are normal, thereby initializing various integrated circuits and driving a spindle motor for rotating the magnetic disk. However, if any one of the power supply voltages is unstable, the power supply monitor circuit supplies the output PF of a logic "LOW" level to the controller. Therefore, the integrated circuits are not initialized and the hard disk drive can not be used. A permissible voltage variation of the power supply voltage of 12V is adjusted to 10.8V (-10%) by using the ratio of two resistors, and the voltage variation of the power supply voltage of 5V is adjusted to 4.5V (-10%) by using the ratio of resistors. As one of the factors giving rise to a unstable power supply voltage, there is an activation current supplied initially to the spindle motor in order to rotate the magnetic disk at a constant velocity. The activation current is about 1 ampere and makes the power supply voltage unstable since a high current is instantaneously drawn. In more detail, if the spindle motor instantaneously draws a large amount of current, the power supply voltage Vcc monitored by the power supply monitor circuit is lowered to a voltage less than its permissible variation voltage, due to the high current. In this case, the output PF of the power supply monitor circuit is also instantaneously lowered to a logic "LOW" level and such an output is supplied to the controller. Hence, there is a malfunction in initializing the integrated circuits.
The patent to Blagaila et al., U.S. Pat. No. 5,457,365, entitled Disk Drive Power Management System, discloses a system in which the drive current for the hard disk motor is limited so that the supply voltage does not fall below a predetermined limit greater than the shut down voltage of the power supply monitor.
The patent to Yamasaki et al., U.S. Pat. No. 5,339,446, entitled Power Supply And Method For Use In A Computer System To Confirm A Save Operation Of The Computer System And To Stop A Supply Of Power To The Computer System After Confirmation, discloses a system which shuts off the power to a hard disk drive in a predetermined sequence to prevent damage to the hard disk drive.